The present invention relates generally to mine stoppings and mine doors, and more particularly to relief doors for relieving air pressure against mine doors.
“Stoppings” are widely used in mines to stop off the flow of air in passageways in the mines, a stopping generally being a metal or masonry (e.g., concrete block) wall installed at the entrance of a passageway to block flow of air therethrough. Such stoppings are typically provided with a doorway or opening and a door therein for occasional access to the blocked-off passageway. Co-assigned U.S. Pat. No. 5,240,349, which is incorporated herein by reference, shows power-operated mine door systems mounted in such stoppings. The door system comprises a door frame 22 defining a doorway and two door leafs 24, 28 hinged on the door frame. The door leafs are opened by power means comprising hydraulic cylinders 94, 96 mounted on supports attached to the door frame.
Doors used in mines operate under conditions not usually encountered by typical doors. Mine doors are subject to large forces due at least in part to air flow in the mine and consequent air pressure differentials on opposite sides of the door. Each mine door leaf can be as large as 10 feet wide and 20 feet high, and weigh more than a thousand pounds when designed for a peak air pressure differential of 7 inches water gauge (IWG) and over two thousand pounds when designed for a peak pressure differential of 20 IWG. Therefore, the mine door leafs can be subject to large forces from the large air pressure differential on opposite sides of the leafs. The large forces require the use of expensive, powerful door operating mechanisms.